Method of making well logging apparatus

ABSTRACT

A replaceable insulating sleeve is disposed around the lower end of a drill string used in drilling a well. The sleeve is restrained from rotating relative to the drill string, but can be released and quickly slipped off the drill string in the field to permit rapid replacement if damaged, or if alternate equipment is required. The sleeve carries sensing means for measuring a characteristic of formations penetrated by the well.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to apparatus for logging wells during drillingand to methods for making such apparatus.

2. The Prior Art

Although the advantages of simultaneously drilling and logging aborehole have long been recognized, such services have developed slowlybecause of the lack of reliable equipment which can be quickly repairedor replaced in the field.

Many prior art patents disclose various types of electrically insulatedsleeves fitted around the drill string with instrumentation just abovethe drill bit in an attempt to measure while drilling such variables asformation electrical resistivity, self-potential, temperature, pressure,radioactivity, directional deviation of a drill hole, and the like.Examples of such apparatus are shown in U.S. Pat. No. 2,568,241 toMartin, U.S. Pat. No. 2,930,137 to Arps, U.S. Pat. No. 3,149,683 toClements et al, and U.S. Pat. No. 3,293,542 to Piety.

The disadvantage of the sleeves previously proposed for logging whiledrilling is that they cannot be readily removed and replaced in thefield, which severely limits their utility.

SUMMARY OF THE INVENTION

This invention provides an insulating sleeve which can be easily andquickly secured around a drill string above the drill bit, and also bequickly and easily removed and replaced by another sleeve if the firstsleeve should become damaged, inoperative, or inapplicable for aparticular well-logging problem.

Briefly, this invention provides well logging apparatus which includes ahousing having a longitudinal opening extending through it. Means areprovided at each end of the housing for securing it in a drill string ina well. A replaceable sleeve of electrical insulating material isdisposed around the housing, preferably in the vicinity of the drillbit. Means are provided for preventing the sleeve from rotating relativeto the housing and yet permit the sleeve to slide longitudinally so itmay be easily slipped on or off the housing. Means are provided at oneend of the sleeve to prevent the sleeve from sliding longitudinallyrelative to the housing in one direction, and removable means at theother end of the sleeve prevent it from sliding longitudinally relativeto the housing in the opposite direction. Sensing means on the sleevemeasure a characteristic of formations penetrated by the well.

In a presently preferred embodiment, the housing is generallycylindrical, one end of the housing is stepped down to a reduceddiameter, and the sleeve is disposed around that end. The shoulder wherethe housing changes diameter limits the longitudinal movement of thesleeve relative to the housing toward the larger-diameter end.Preferably, the external diameter of the sleeve is about the same asthat of the unreduced section of the housing. The preferred embodimentalso includes a wear ring disposed around the housing between theshoulder and the adjacent end of the sleeve. Means are provided toprevent the wear ring from rotating relative to the housing, and yet letthe sleeve slide longitudinally. Preferably, releasable locking meansare provided to restrain the ring against sliding.

Preferably, a torque tube is disposed around the reduced diameterportion of the housing adjacent the end of the sleeve remote from thehousing shoulder. Suitable means on the torque tube and adjacent portionof the housing prevent the torque tube from rotating relative to thehousing, yet permit longitudinal movement of the torque tube along thehousing. Means independent of the sleeve are provided for preventing thetorque tube from sliding along the housing toward the shoulder in casethe sleeve is worn away during drilling.

Mating grooves and splines on the wear ring, sleeve, torque tube, andhousing are the presently preferred structure for preventing the wearring, sleeve, and torque tube from rotating relative to the housing, andyet permit relative longitudinal movement of those elements along thehousing.

The sensing means on the sleeve can be any of a variety of devices, suchas electrodes for measuring formation electrical resistivity,self-potential, or inductive reactance. The sensing means can be otherdevices, such as piezoelectric crystals for measuring acousticproperties of adjacent formations in the well bore, or sensors formeasuring temperature, pressure, strain, or the like. Means are providedfor supplying electrical power to generate signals and for measuring andrecording the signals.

In terms of method for fabricating an electrode assembly for attachmentto a drill string, the invention includes the steps of forming a sleeveof insulating material having at least one electrical conductor embeddedin the sleeve; forming at least one recess in the outer surface of thesleeve; exposing the electrical conductor in the recess; and depositingmetal within the recess to at least partly fill it and make electricalcontact with at least part of the exposed conductor. Preferably, themetal is deposited by spraying it into the recess in a molten state andallowing it to solidify.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional elevation of the invention mounted in a drillstring in a well bore;

FIG. 2 is a view taken on line 2--2 of FIG. 1;

FIG. 3 is a view taken on line 3--3 of FIG. 1;

FIG. 4 is a view taken on line 4--4 of FIG. 1;

FIG. 5 is an enlarged sectional elevation taken on line 5--5 of FIG. 4,and in which the housing is not shown;

FIG. 6 is an enlarged sectional elevation taken on line 6--6 of FIG. 4;

FIG. 7 is an enlarged view taken in the area of 7--7 of FIG. 1;

FIG. 8 is an enlarged view taken in the area of 8--8 of FIG. 1;

FIG. 9 is an end view of the wear ring;

FIG. 10 is a view taken on line 10--10 of FIG. 9;

FIG. 11 is a schematic sectional elevation of a portion of the sleevebefore the application of electrode material;

FIG. 12 is a view similar to FIG. 11 showing electrode material appliedto the sleeve; and

FIG. 13 is a view similar to FIGS. 11 and 12 showing the electrode in afinished condition.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to FIG. 1, an elongated, cylindrical, hollow sleeve 20 makes aclose slip-fit over a lower section 22 of an elongated, generallycylindrical housing 24 having a central longitudinal bore 26 extendingthrough it. The housing includes upper section 27 of larger outsidediameter than the lower section 22, so that an annular, downwardlyfacing (as viewed in FIG. 1) shoulder 28 is formed where the largersection 27 steps down to the smaller diameter of lower section 22. Thehousing is part of a drill string 29 disposed in a well bore 30.

An annular wear ring 31 makes a close slip-fit around the smallerdiameter section 22 of the housing so that the upper surface of the wearring bears against shoulder 28. The lower surface 32 of the wear ringslopes downwardly and outwardly to rest on a matching surface at theupper end of the sleeve.

An upper electrode ring 34 is disposed in an upper circumferential andoutwardly opening groove 36 in the outer surface of the sleeve. A lowerannular electrode 38 is disposed in a lower circumferential andoutwardly opening groove 40 in the outer surface of the sleeve.

The upper and lower electrodes are connected by separate electricalconductors 42 (one such conductor is shown in FIGS. 11-13) in a cable44, which extends up through the insulated sleeve and a cable tunnel 46formed through the wear ring and the wall of the housing.

The upper end of the cable is connected to a power and instrumentpackage 48, which includes an electrical power source (not shown) andappropriate equipment (not shown) for generating, measuring, andrecording signals developed in response to various physicalcharacteristics of the adjacent formation in the well bore. The powerand instrument package is secured in the center of the central bore 26of the housing by three equally spaced and radially extending spiders 50secured at their inner ends to the power and instrument package. Theouter ends of the spiders bear against the interior surface of the borethrough the housing. The lower edges of the spiders rest on an annularand upwardly facing internal shoulder 52 formed within the bore 26 inthe housing. As shown in FIGS. 1 and 2, the cable tunnel includes ahorizontal section 54, which extends from the power and instrumentpackage through one of the spiders to join the upper end of the verticalportion of the cable tunnel in the wall of the housing.

The lower end of the insulated sleeve has a downwardly and inwardlyextending annular surface, which rests on a matching surface 62 on theupper end of a torque tube 64, which makes a close slip-fit around thelower portion of the housing. The lower end of the torque tube rests onan upwardly facing annular shoulder 66 at the upper end of a drillcollar section 68, into which the lower end of the housing is threaded.The upper end of the housing is threaded onto the lower end of a sectionof drill collar 70 in the drill string.

As shown in FIG. 3, the insulating sleeve includes four equally spaced,inwardly projecting, and longitudinally extending splines 72, which eachfit into a respective matching outwardly opening and longitudinallyextending groove 74 in the outer surface of the housing. The splines onthe insulated sleeve extend for the full length of the sleeve. Thegrooves in the exterior surface of the housing extend from about themidpoint of the wear ring to the lower end of the torque tube, which hasfour equally spaced, inwardly projecting splines 76 (FIG. 4) whichextend longitudinally for the length of the torque tube and fit into thehousing grooves.

In effect, the splines 72 on the sleeve form a separate longitudinallyextending groove 77 between adjacent splines, and the grooves 74 in thehousing form a separate longitudinally extending spline 78 betweenadjacent grooves.

The bottom surfaces of the grooves and the top surfaces of the splinesof the sleeve and the housing taper inwardly away from the shoulder tofacilitate assembly and disassembly of the sleeve on the housing. Theamount of taper can vary over a wide range, but we have found that arelatively slight taper, say, about 1/8" in 13 feet, is adequate toprovide an easy, but close slip-fit of the sleeve on the housing.

The splines 76 on the torque tube form a separate longitudinallyextending groove 79 between adjacent splines. The grooves and splines ofthe sleeve and torque tube make a close slip-fit with the grooves andsplines of the housing so the torque tube is firmly supported againstrotation relative to the housing, but is easily moved longitudinallywhen necessary.

Referring to FIG. 5, which is a view taken on line 5--5 of FIG. 4 (withthe housing not shown), a wire retaining ring 80 is disposed in fourinwardly opening, circumferential grooves 82 formed in the lower ends ofthe torque tube splines 76, so the wire is secured under an outwardlyextending and downwardly facing shoulder 84 (FIG. 6), where the o.d. ofthe housing is reduced for a short, vertical section 86 adjacent theupper end of the lower drill collar section 68. The retaining ring 80prevents the torque tube from sliding upwardly along the housing if theinsulated sleeve should be worn away during drilling operations.

Referring to FIG. 7, the wear ring is prevented from sliding downwardly(if the insulated sleeve should be worn away during drilling operations)by a bolt 90 threaded into the housing wall to project outwardly intothe inner end of a bore 92 extending radially through the wear ringwall. More than one such bolt can be used, if desired. Three inwardlyand longitudinally extending splines 93 (FIGS. 9 and 10) on the innersurface of the lower half of the wear ring each fit into a respectivegroove 74 in the outer surface of the housing to prevent the wear ringfrom rotating on the housing, and yet leave the wear ring free to slidelongitudinally when the bolt 90 is removed.

As shown best in FIG. 8, the upper end of the electrical cable 44extends from the upper end of the insulating sleeve into alongitudinally extending slot 94 (FIGS. 9 and 10) in the interiorsurface of the wear ring. As shown in FIG. 9, the slot 94 is spaced 90°from two of the wear ring splines 93, which are each spaced 90° from thethird spline. Thus, the three wear ring splines each form a separaterespective groove 95 between adjacent splines, the groove which includesslot 94 being twice as wide as the other two. Accordingly, the groovesand splines of the wear ring make a close slip-fit with all four of thesplines on the housing, but with only three of the grooves in thehousing because of wear ring slot 94. This is adequate support torestrain the wear ring from rotating relative to the housing.

The upper end of the cable carries a connector plug 96, (FIG. 8), whichreleasably fits into a socket 98 sealed in the lower end of the verticalportion of the cable tunnel 46 in the wall of the housing to preventincursion of drilling fluid into the power and instrument package. Theplug 96 is provided with suitable sealing means (not shown), which maybe of conventional construction, to prevent incursion of high-pressurefluids from the well bore into the electrical connections made by theplug with the socket.

The material which forms the insulated sleeve must withstand hightemperatures and shock. It must also have reasonably good wearresistance to the abrasive conditions encountered during the drilling ofmost wells, and it must have high electrical resistivity to avoidunacceptable leakage between the drill string and electrodes or othersensing devices on the sleeve. These requirements are met by forming theinsulating sleeve from glass fibers and epoxy resin, which includesparticles of abrasion-resistant material, such as aluminum oxide soldunder the trademark "Carborundum". U.S. Pat. No. 3,072,843 to Clementset al describes the use of such materials to form an electrode sleeve ona drill pipe.

We have prepared suitable insulating sleeves by wrapping glass fiberscoated with epoxy resin and Carborundum particles around a mandrel (notshown) which matches the surfaces of the portion of the housing aroundwhich the insulated sleeve is to fit. During the wrapping operation, theappropriate electrical conductors are embedded in the wall of theinsulating sleeve as it is formed. The top and bottom surfaces of thesplines and grooves of the mandrel taper toward one end to match that ofthe housing. Accordingly, after the resin has cured, the formed sleevecan be easily slipped off the mandrel, and the internal surfaces of thesleeve are tapered to match those on the housing.

The principal steps in making an electrode sleeve assembly, say, usefulfor electric well logging, are shown in FIGS. 11-13. Outwardly opening,circumferential grooves 40 (only one groove is shown in FIGS. 11-13) areformed in the outer surface of the sleeve to reach the end of one of theconductors 42 embedded in the sleeve wall during the production of thesleeve. The end of the conductor is raised into the groove and strippedof insulation to expose bare metal.

As shown in FIG. 12, a metallic conductor material 100 is deposited inthe prepared groove to invest the exposed end of the conductor. Thedeposited metal may be sprayed into place by the well-known Metcoprocess. It may also be electrodeposited, accumulated by vapordeposition, or any combination of such processes. Spray deposition ispresently preferred. As shown in FIG. 13, the deposited metal issmoothed so that its outer surface is flush with the outer surface ofthe sleeve, leaving an annular electrode 38.

In using the replaceable sleeve of this invention, it is assembled asshown in FIG. 1, so that it is firmly supported on the housing andclamped between the wear ring at its upper end and the torque tube atits lower end. The torque tube is made of steel of sufficient strengthto accept the wear and stress imposed by conventional tongs (not shown)when the housing is threaded into, or out of, a drill collar. Theannular shoulder 66 on the drill collar holds the torque tube in a snugfit against the sleeve, which is thereby placed in slight, but firm,compression for the drilling operation. The torque tube accepts all ofthe mechanical wear and tear in connecting or disconnecting the housingin the drill string.

Although the insulated sleeve can vary in length for different uses, formost well logging operations, it will be between about 2 and about 15feet long. If it is relatively short, say, only a foot or two, thetorque tube may be omitted, letting the lower end of the electrodesleeve bear directly against the shoulder 66 on the drill collar section68. Under these circumstances, the tongs, normally used to make up orbreak apart drill string, would have to be shifted upwardly from theirnormal position to engage the housing above the insulating sleeve. Ifthe sleeve is more than a few feet long, it normally would not befeasible to raise the tongs sufficiently high to avoid contact with thesleeve. Accordingly, the torque tube is almost always required forpractical operations.

Although the insulating sleeve in the specific embodiment describedabove is built to facilitate measuring the electrical resistivity offormations traversed by the well bore, the sleeve can be provided withother sensing devices for measuring other characteristics of theformations. For example, piezoelectric crystals can be embedded in thesleeve to measure acoustical properties, or other sensors can be used tomeasure pressure, temperature, or borehole deviation during thedrilling.

An important advantage of this invention is that the insulating sleevecan be quickly and easily assembled on, or removed from, the primaryhousing. This is essential in most drilling operations where delays inhandling equipment at a drilling rig are expensive and sometimesdangerous.

If the insulated sleeve is damaged or worn away during drillingoperations, the wear ring protects the annular shoulder 28 on thehousing from damage. The retaining ring in the lower end of the torquetube prevents the tube from sliding up and down the housing, avoidingpossible damage to the housing or the wear ring.

In the course of prolonged use, the wear ring may eventually be so wornor damaged that it no longer protects the shoulder or holds theinsulated sleeve in the desired position on the housing. The wear ringis then easily removed and replaced by a new one.

If desired, a second wear ring of appropriate size and shape can bedisposed between the torque tube and the lower end of the insulatedsleeve to prevent damage to the upper end of the torque tube when theinsulated sleeve is worn away.

The insulated sleeve is easily replaced by simply slipping it off thelower end of the housing after the housing is removed from the drillcollar section 68, and the torque tube is slipped off the lower end ofthe housing. The electrical plug 96 (FIG. 8) is disconnected by removingthe bolt 90 (FIG. 7) from the bore 92 in the wear ring wall so the wearring and insulating sleeve can be lowered a few inches to provide accessto the plug 96, which is then removed. A similar plug (not shown) on areplacement sleeve (not shown) is connected to the socket 98 and sealedthereto by appropriate means (not shown). The wear ring is then raisedback to its position against shoulder 28 on the primary housing andlocked in place by inserting the bolt 90, which has an internal hexsocket 101 to facilitate screwing the bolt into and out of the housingwall. The torque tube is slipped over the lower end of the housing tothe position shown in FIG. 1. The tongs are applied to the torque tube,and the lower end of the housing is threaded into the upper end of thedrill collar section 68 until the torque tube, insulated sleeve, andwear ring are snugly fitted together as shown in FIG. 1.

With the apparatus assembled as shown in FIG. 1, it can be used to logthe electrical resistivity of formations traversed as the well isdrilled. The logging information can be either recorded with equipment(not shown) in the power and instrument package, or it can betransmitted to the surface during drilling by generating coded pressurepulses in the drilling fluid, such as described in U.S. Pat. No.3,964,556 to Gearhart et al or U.S. Pat. No. 4,078,620 to Westlake etal.

From the foregoing description, it will be apparent that this inventionprovides an insulated sleeve which can be quickly and snugly fittedaround a portion of the drill string so the sleeve is not rotatablerelative to the drill string, and so the sleeve can be quickly slippedoff the drill string, when required.

We claim:
 1. A method for making an electrode assembly adapted to slideon and off a drill string to be used in a well for measuring electricalresistivity of earth formations traversed by the well, the methodincluding the steps of:(a) forming a sleeve of insulating material bywrapping resin-coated fibers around an elongated and generallycylindrical mandrel, the mandrel having an exterior surface whichconverges toward one end so the sleeve is formed with an internalconverging surface matching the external surface of the mandrel; (b)embedding at least one electrical conductor in the sleeve; (c) forming arecess in the outer surface of the sleeve to expose the embeddedelectrical conductor in the vicinity of the recess; (d) depositing metalwithin the recess to at least partially fill it and make electricalcontact with at least part of the exposed electrical conductor; (e)curing the resin while the fibers are wrapped around the mandrel; and(f) thereafter slipping the sleeve from the mandrel and thereafterslipping the sleeve onto a drill string having an external surfacematching that of the mandrel.
 2. A method according to claim 1 in whichthe formation of the recess includes forming an outwardly opening,circumferential groove in the outer surface of the sleeve.
 3. A methodaccording to claim 1 or 2 in which the external surface of the mandrelincludes longitudinally extending grooves and splines with surfaceswhich converge toward one end of the sleeve.
 4. A method for making alogging assembly adapted to slide on and off a drill string in a wellfor measuring a downhole characteristic in the well, the methodincluding the steps of:(a) forming a sleeve of insulating material bywrapping resin-coated fibers around an elongated and generallycylindrical mandrel, the mandrel having an exterior surface whichconverges toward one end so the sleeve is formed with an internalconverging surface matching the external surface of the mandrel; (b)embedding at least one electrical conductor in the sleeve; (c) securingsensing means to the sleeve; (d) connecting the electrical conductor tothe sensing means; (e) curing the resin while the fibers are wrappedaround the mandrel; and (f) thereafter slipping the sleeve from themandrel and ther after slipping the sleeve onto a drill string having anexternal surface matching that of the mandrel.